216 (#288) ############################################ WOOLLEN AND WORSTED SPINNING Hold the fibre very firmly and yet without any likelihood of grinding or cutting; Present the fibres to the front rollers (aided by fallers, porcupines or carriers) in such a way that they control the fibres until the front rollers take hold and draw the fibres out at the increased drafting speed ; and finally The speeding must be readily under control so that according to the qualities of wool to be treated the drafts required may be readily obtained along with satisfactory control of the fibres composing the slivers. In studying pairs of rollers in combination it will be necessary to consider- The material and build of rollers (top and bottom); The surfaces of rollers (flutings, milled sur- face, etc.); The nature of roller coverings and the method adopted of roller covering ; The sizes and relative sizes of rollers (top and bottom), and The weighting-simple and complex-of rollers. Finally, with reference to drawing boxes it will be necessary to consider- The relative sizes of back and front rollers ; The adjustment of back and front rollers and gills, porcupines or carriers to control drafting; and The angle of roller inclination and the angle of delivery of the sliver to the spindle. The casting of rollers either singly or on a central shaft, the building up of the larger rollers and the turning, for truth of "surface,” of all rollers must be passed over here, but definite reference must at least be made to the materials of which rollers consist. Those accustomed to work woollen mules know that 216